This invention relates to multi-speed planetary type power transmissions and, more particularly, to planetary transmissions providing at least seven forward speed ratios and one reverse speed ratio.
Automatic shifting power transmissions are currently used in a majority of the vehicles produced in the United States. These vehicles generally employ three- and four-speed power transmissions. More recently, a trend towards more ratios, such as five- and six-speed power transmissions, has been proposed. In fact, some manufacturers do provide five-speed transmissions. Many of the vehicles utilizing manual type transmissions or countershaft type transmissions employ five- and six-speed power transmissions.
The five- and six-speed power transmissions provide improved vehicle acceleration performance and fuel economy when compared with three- and four-speed transmissions. Seven-speed power transmissions offer further improvements in vehicle acceleration performance and fuel economy over six-speed transmissions, but they have not been proposed due to the complexity of these assemblies, as well as size and cost. There are many current patents that describe five- and six-speed power transmissions. Some of the six-speed power transmission patents, especially those assigned to the assignee of the present invention, describe six-speed power transmissions in families, wherein one or more family members incorporate a seven-speed power transmission, but many of these seven-speed transmissions do not offer very good ratio progressions.
It is an object of the present invention to provide a low content seven-speed power transmission with good ratio progressions requiring three planetary gearsets and six actively engageable transmission mechanisms.
In one aspect of the present invention, the number of planetary gearsets utilized in the planetary gear arrangement is held at three planetary gearsets.
In another aspect of the present invention, a family of seven-speed power transmissions utilizes six torque-transmitting mechanisms which are represented by four clutches and two brakes, or five clutches and one brake.
In another aspect of the present invention, each planetary gearset employs three members comprised of sun gear members, ring gear members, and planet carrier assembly members.
In yet another aspect of the present invention, the first member of the first planetary gearset is continuously interconnected with the first member of the second planetary gearset.
In still another aspect of the present invention, a second member of the second planetary gearset is continuously interconnected with a first member of the third planetary gearset through a fixed interconnection.
In yet still a further aspect of the present invention, the output shaft of the transmission is continuously connected with at least one member of one of the planetary gearsets.
In yet still another aspect of the present, a first and second of the rotating torque-transmitting mechanisms selectively interconnect the input shaft with members of the planetary gearsets or one of the fixed interconnections.
In a further aspect of the present invention, a third of the torque-transmitting mechanisms selectively interconnects a member of one of the planetary gearsets with the output shaft, or another member of one of the planetary gearsets.
In yet a further aspect of the present invention, a fourth of the torque-transmitting mechanisms selectively connects a member of one of the planetary gearsets with another member of one of the planetary gearsets.
In a still further aspect of the present invention, a fifth of the torque-transmitting mechanisms selectively connects a member of one of the planetary gearsets with a stationary member of the transmission, such as a transmission housing.
In a yet still further aspect of the present invention, a sixth of the torque-transmitting mechanisms selectively interconnects a member of the first or third planetary gearset with another member of one of the planetary gearsets, or selectively connects a member of one of the planetary gearsets with a stationary member of the transmission.
In a yet still further aspect of the present invention, the six torque-transmitting mechanisms are selectively engageable in combinations of four to establish at least seven forward speed ratioSand one reverse speed ratio between an input shaft and the output shaft of the transmission.
By utilizing only three planetary gearsets and six torque-transmitting mechanisms, which are arranged between an input shaft and an output shaft of the power transmission, the present invention has therein a minimum of mechanical components, which must be assembled in a transmission housing. Thus, the transmission assembly is no more complex, except for one additional torque transmitting mechanism, than many of the five- or six-speed power transmissions presently proposed as useful in automobiles. Moreover, the present invention provides for a family of transmissions, incorporating the minimum mechanical component requirement and offering good ratio progressions.
It is also an advantage of the present invention, that each of these transmissions provides single transition interchanges between adjacent forward speed ratios. This greatly simplifies the control function of the transmission since it is only necessary to disengage one torque-transmitting mechanism while engaging the other. Those skilled in the art will recognize that this is the control function generally found in most of today""s useful automatic power transmissions.